not sure where to start with this request but I'll ask the obvious, just to make sure...
Is your monitor calibrated?
If not calibrated with some sort of colorimeter and set to an appropriate overall intensity and gamma then it should be at least set up to view sRGB images such that you can see the differences between all the different RGB intensities that would make up an image. The last few extreme light and dark levels are often going to be clipped or hard to distinguish but you should have discernible tonality over everything else.
Many people have their monitors set too bright and contrasty. This can make underexposed images look good and properly exposed ones look a bit too bright.
try this page as a starting point:
www.imaging-resource.com/ARTS/MONCAL/CALIBRATE.HTM
don't forget the effect of ambient light on your display as well. And if you have your display set to automatically adapt its brightness to the ambient light it could be making things worse instead of better.